Human T-cell lymphotropic virus type I (HTLV I) has been identified as the etiological agent responsible for adult T-cell leukemia/lymphoma (ATLL). It has also been associated with a chronic neurological disorder known as tropical spastic paraparesis (TSP) or HTLV-associated myelopathy (HAM) (Reitz et al., 1983, J. Infect. Dis. 147:399-405; Gessain et al., 1985, Lancet, ii:407-410). The virus can be transmitted by blood transfusion, intravenous drug abuse, sexual contact and through breast feeding, and infection is endemic in southwestern Japan, Central Africa, and in parts of the Caribbean. The virus has also been found in North America and Europe.
The closely related human T-cell lymphotropic virus type II (HTLV II) is not definitely implicated in human disease, although it has been identified in two cases of atypical hairy cell leukemia (Kalyanaraman et al, 1982, Science, 218:571-573), HTLV II-like sequences have been detected in patients with chronic fatigue immune dysfunction syndrome (CFIDS) (DeFreitas et al, Proc. Natl. Acad. Sci. USA 88:2922-2926,1991) and an HTLV II virus has been isolated from cultured T cells of a patient with pancytopenia (Kalyanaraman et al, The EMBO Journal 4:6:1455-1460, 1985). The epidemiology of HTLV II infections is also distinct, being primarily associated with intravenous drug abuse and a focus of HTLV II endemicity has been reported among the native Guaymi Indians of Panama (Heneine et al, 1991, New Eng. J. Med. 324:565).
There is no viremia throughout the course of infection with HTLV I or II, i.e., the circulating viral genome (i.e., RNA) cannot be detected. Polymerase chain reaction (PCR) has been shown to be capable of detecting proviral sequences and to distinguish between HTLV I and HTLV II proviruses (Tuke et al., J. Virological Methods, 40:163-174, 1992). While it is possible to detect the integrated provirus, it has been difficult to detect mRNA and therefore determine the role of viral gene expression in development and maintenance of the disease state. Screening of patient PBMC by RT/PCR has been used for the detection of the HTLV I tax transcript in the PBMC of asymptomatic patients as well as infected individuals displaying disease, but this assay did not detect HTLV II transcripts (Breneman et al, PNAS 89:3005-3009, 1992).
In view of the very different prognoses associated with HTLV I and HTLV II infection, it is important to be able to distinguish between the two viruses for the purposes of screening of blood donors, epidemiological studies, and routine clinical practice. Serological tests have been attempted, but because of high amino acid sequence homology, such tests have not been able to differentiate the two viruses with certainty (Kline et al, 1991, Lancet 337:30-33).
An isothermal amplification method for the detection of HTLV RNAs has not been described. The isothermal method of the present invention for HTLV I and II provides an effective method of screening for the presence of several viral transcripts or viral genome and is able to distinguish between the two viruses.